1. Field of the Invention
This invention relates, generally, to a biodegradable tissue marker and sealant. More particularly, it relates to a tissue marker formed of a biodegradable polymer having drug-delivery capabilities. It further relates to a sealant that encapsulates the tissue marker and which serves to help anchor the tissue marker against migration.
2. Description of the Prior Art
U.S. Pat. No. 6,350,244 entitled Bioabsorable Markers For Use In Biopsy Procedures to the present inventor discloses a bioabsorbable marker that is positioned near a lesion or tumor during a biopsy procedure. The marker includes a contrast agent and is bioabsorbed slowly so that the biopsy site can be located weeks or even months later if needed. U.S. Pat. No. 6,350,244 is hereby incorporated by reference into this disclosure, and is hereinafter referred to as the first-incorporated patent.
Co-pending U.S. patent application Ser. No. 09/683,282, filed Dec. 7, 2001, entitled Bioabsorbable Sealant, also to the present inventor, discloses a sealant that expands upon contact with water or other bodily fluid. It can also expand upon contact with heat or other stimulus. The sealant has utility in sealing various openings in the body such as a hole in a lung, an opening in the myocardial septum, and the like. It is also useful in sealing a blind bore that contains stem cells that promote angiogenesis. U.S. patent application Ser. No. 09/683,282 is also hereby incorporated by reference into this disclosure, and is hereinafter referred to as the second-incorporated disclosure.
Prior to this disclosure, it was not known that the tissue marker of the first-incorporated disclosure and the sealant of the second incorporated disclosure could be combined and used in combination with one another. Anchoring the tissue marker against migration was problematic. Moreover, although the tissue marker included a contrast solution to facilitate its imaging under X-rays, it was unknown how to use the tissue marker or the sealant as a drug delivery means.
Nor was it known that a tissue marker could be formed into a shape that would enable it to serve as its own anchoring means.
Nor was it known how polymers having utility as tissue markers could be formulated to achieve differing degradation rates. More particularly, it was not known how to make different polymers to contain contrast for different amounts of time, such as one month to six months or more by using two different polymers.
Nor was it known how to formulate a marker polymer with a therapeutic drug or other pharmaceutical agent so that the degradation of the marker would gradually release the drug or agent to a site.
Nor was it known how the polymers could be formulated to exhibit differing expansion rates when exposed to water or other liquid fluids.
The sealants of the prior art require in-situ curing. For example, Focal Sealant® is an in-situ sealant available from Genzyme Corporation. Prior art sealants such as Focal Sealant require the application of a stimulant such as visible light, heat, and the like thereto.
Accordingly, what is needed is a combination tissue marker and sealant that can be formed into many different shapes and sizes, depending upon the application, that can degrade at different rates, depending upon the application, that can expand in response to moisture or other bodily fluids at different rates, depending upon the application, and that does not require in-situ curing.
There is a need as well for a bioabsorbable tissue marker that can deliver drugs or other therapeutic agents to a site over a prolonged period of time.
There is a further need for a sealant that can anchor a tissue marker against migration, that can provide a seal for openings in tissue, and that biodegrades over a period of one to six months or more.
Moreover, there is a need for a combination tissue marker and sealant that requires no in-situ curing as aforesaid and which therefore requires no initiators, buffers or other chemicals, proteins, enzymes, visible light, UV, accelerator, nor addition of foreign chemicals into the body.
A need also exists for a means for making tissue markers more compatible with surrounding tissue. Tissue markers are hard and have little compatibility with surrounding tissue. Thus there is a need for a cushioning means that surrounds a marker and which provides a more compatible interface means with surrounding tissue.
Biodegradable polymers in general have been used in many medical devices and implant applications. For example, they have been used as orthopedic implants, tissue sealants, sutures, and as ligating clips. The medical devices incorporating these polymers are made, primarily, of biodegradable materials such as poly(dioxanone) (PDO), polyethylene glycol (hydrogels, polylactides (PLA), polyglycolides (PGA), polycaprolactone (PCL), and their copolymers. Some of the polymers, such as hydrogels, are hydrophilic. Others such as PCL are hydrophobic. Because these polymers degrade by hydrolysis, the type of polymer and its physical form used in a particular application has an effect in defining the degradation period.
Traditional brain tumor treatment includes surgery, radiotherapy, and chemotherapy. Alternative strategies are needed due to the high rate of recurrence of tumors after such treatment and their resistance to radiation and cytostatics. In the recent past, gene therapy treatments such as reversion of the malignant phenotype by down regulation of the oncogene expression or insertion of normal tumor genes have been tried. One challenge with gene therapy treatments concerns the prevention of immunorejection of genetically modified cells after intracranial implantation. A further challenge is to achieve efficient gene transfer, as well as prolonged gene expression within the relevant cells.
Numerous other surgical procedures would be facilitated by tissue markers that degrade over predetermined periods of time, that include contrast agents so that they can easily be found, that do not migrate, that interface well with surrounding tissue, and that deliver drugs or other therapeutic agents to a site over a predetermined length of time.
In view of the prior art considered as a whole at the time the present invention made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.